Firestore 子集合删除文档中最旧的

Question

I've been struggling with figuring out how to delete documents from a sub collection, keep only the latest 5 documents.

I firstly try and get a list of documents in the sub collection, ordered by 'updated' date timestamp. This however returns null

let updates = await firestore
    .collection('spots')
    .doc(spot.id)
    .collection('spotupdates')
    .orderBy('updated','desc');

I then try and delete the oldest from the list, to ensure only 5 remain

var cntr = 0;
while(updates.docs.length > 5){
    await firestore
        .collection('spots')
        .doc(spot.id)
        .collection('spotupdates')
        .doc(updates[cntr].id)
        .delete();
    cntr++;
}
cntr = null;

Please help - really stuck

Answer 1

According to Firebase Documentation for deleting data from your database:

To delete an entire collection or subcollection in Cloud Firestore, retrieve all the documents within the collection or subcollection and delete them. If you have larger collections, you may want to delete the documents in smaller batches to avoid out-of-memory errors. Repeat the process until you've deleted the entire collection or subcollection.

You may find a simplified code snippet to delete collections and subcollections in this link .

Also you will find more information and detailed examples about deleting fields, documents and collections in Firestore in this link .

Let me know if this was helpful.

Answer 2

I did something similar on my app but based on your data structure

First, get all the documents in the collection

const updates = await firestore
                 .collection('spots')
                 .doc(spot.id)
                 .collection('spotupdates')
                 .get()

Map the document data to return an array

const updatesArray = updates.docs.map(doc => doc.data())

Do logic then delete

if (updatesArray.length > 5){
            const sorted = updatesArray.sort((a,b) => b.created_at - a.created_at)
            const oldest = sorted.pop()
            await firestore
             .collection('spots')
             .doc(spot.id)
             .collection('spotupdates').doc(oldest.id).delete()
        }